They do have ads[1], but they don't use (or have) tracking data for it.

1: https://help.duckduckgo.com/company/advertising-and-affiliat...

Sorry I have to disagree. I use DuckDuckGo for year by now and 60% of the time I add !g to my queries. It is slowly improving over time but not quite yet there.

It's free but the quality of search results is very poor.